Electronic control of engines for automotive and related applications has become more precise and sophisticated as fuel economy and environmental regulations have become more stringent. Most control schemes involve calculation of controllable variables in real time based upon prestored constants and inputs from sensors that monitor engine operation. U.S Pat. No. 4,551,803 is exemplary of systems of this type, in which variation of the control process involves adjustable control of the equation constants. Calculations are employed in both open-loop operation during warm-up of the engine, and in closed-loop operation under normal operating conditions when an oxygen sensor in the engine exhaust is employed for sensing engine air/fuel ratio. A problem with control schemes of this character lies in the time required to calculate the controllable variables based upon the sensor inputs and prestored constants.
To help alleviate the time constraints of this variable calculation technique, it has been proposed to employ look-up tables rather than time-consuming calculations to obtain control parameters during engine operation. Initially, it was proposed to employ look-up tables in open-loop control during engine warm-up. A serious problem and limitation of such systems lies in the requirement that the tables be permanently stored in a programmable read-only-memory or PROM that is initially programmed at the factory, and that requires removal and replacement to change or reprogram any of the stored control variables. Although such requirement for removal and replacement at a factory service facility or the like has been considered to be acceptable for normal passenger car and light truck applications in view of EPA requirements that critical engine control parameters not be variable outside of an authorized service environment, such schemes are unacceptable for racing and other off-road applications, and in development and test environments. In applications of these types, it is necessary that the control variables be readily, individually and selectively reprogrammable by a technician or other operator at the site.
U.S. Pat. No. 4,751,633 discloses an engine control system that employs look-up tables in an EEPROM during both warm-up and normal operation. An external programming unit allows reprogramming of the system memory, without requiring removal of the memory package, to accommodate specific vehicle conditions, such as fuel quality, climate, etc. No provision is made for selective variation of table control parameters in memory during actual engine operation.
It is therefore a general object of the present invention to provide a system and method for electronic control of engine operation that features enhanced reprogrammability of engine control variables. Another and more specific object of the invention is to provide a method and apparatus for electronic engine control in which the engine control variables may be readily and selectively varied in real time without interrupting engine operation, so that the operator may readily observe the effects of parameter variation and make any desired further adjustments without necessitating removal of table memory or other electronic circuitry. Yet another object of the present invention is to provide a system and method of the described character in which the control variable tables are displayed to an operator in such a way as to facilitate selective variation of the control parameters, and in which various control tables may be stored externally of the engine for later reuse as desired. A further and yet more specific object of the invention is to provide a method and system for enhanced flexible electronic control of fuel delivery to an internal combustion engine.